Circulation system for wood pulp digesters



Nov. 14, 1939. E. MORTERUD 1179.796

CIRCULATION SYSTEM FOR woon PULP nIc-ss'rnns Filed Oct. 8, 1957 2 Sheets-Sheet 1 Nov. 14, 1939. E. MORTERUD CIRCULATION SYSTEM FOR WOOD PULP DIGESTERS Filed Oct. 8, 1937 2' Sheets-Sheet 2 aura-r scemsw- Patented Nov. 14, 1939 PATENT OFFICE CIRCULATION SYSTEM FOR WOOD PULP DIGESTERS Einar Morterud, Oslo, Norway Application October 8, 1937, Serial No. 168,074 In Norway May 14, 1936 1 Claim.

In wood pulp digesters with positive circulation of the digesting liquor it has been suggested to remove liquor from one or more sieves or screens located approximately midways between .5 the upper and lwer end'of the digester, reintroducing the liquor into the digester at the top or bottom so as to obtain a two-way circulation with a common outlet.

In digesters of this type the distribution of the liquor between the top and bottom inlet into the digester has taken place by means of two valves or cocks, each placed in one of the pipes leading to the top or bottom of the digester.

This way of controlling the circulation requires a great deal of supervision, and even then it is dificult to control the supply of liquor to the top and bottom in accordance with a predetermined ratio between these two currents.

In accordance with the present invention the return currents of liquor to the top and bottom of the digester are controlled by means of a single valve, which is preferably made in the form of a rotatable flap valve.

By moving such flap valve from one extreme f position to another the valve will completely out off one of the currents and leave the passage for the other current tree.

Between the said two extreme positions the flap valve may be adjusted to divide the'current of liquor in two parts, the ratio between which may be read oii on an indicator or the like.

The adjustment of such valve may take place manually by means of a lever attached to the valve spindle and associated with a pointer and some conventional device for securing the lever in any desired position. V l

The adjusting oi the valve may alsotake place automatically in accordance with, a diagram, a time relay or a temperature relay.

- For instance it may be desired at the beginning of the digesting period, particularly when the amount of liquor is small with relation to the amount of pulp, to provide an energetic'supply of liquor at the top. On some later stage a strong current from the bottom and upwards may be desired and in, intermediate periods. it may be desired to use alternate currents from the top and from the bottom. This is all dependent on the size and form of the digester, the ratio be 1 tween pulp and liquor, the quality of the pulp,

the location of the screens and so on.

In accordance with a further feature of the present invention two outlet sieves may be pro- Vided inside the digester, said sieves being placed at a certain distance from each other interdill till

mediate the top and bottom inlets for liquor.

The outlet of liquor through said outlet sieves in accordance with the present invention may be controlled in the same manner as the supply of liquor to the top and bottom intake openings, the two outlet sieves being interconnected by means of a pipe or channel communicating with a single outlet pipe leading to the circulation pump, the connection between the two outlet sieves and the said single outlet pipe being controlled by a rotatable flap valve, which may be adjusted in the same manner as the flap valve controlling the distribution of liquor to the top and bottom intake openings. 1

By using the combination of the said two con- 15 trolling valves it is possible to so direct the currents of liquor through the digester that these currents may pass either from the bottom intake opening to the upper outlet sieve or from the top intake to the lower intake sieve, whereby it is obtained that the paths of the liquor through the digester in the two cases will cross each other, so as to avoid the risk of forming channels in the pulp, through which the greater part of the digesting liquor will pass under ordinary circumg5 stances.

0n the drawings two embodiments of the invention are diagrammatically illustrated, Figure 1 being a. .view of a digester with parts shown in cross section and Figure 2 being a diagrammatical 30 sectional viewoi a digester and a circulation system in accordance with the invention.

In accordance with Figure l thedigester i is provided with an annular outlet screen 2 intermediate its top and bottom. The outlet openings '3 and t at the top and bottom are connected with inlet pipes t and t, which may be provided in the usual manner with cocks or valves l, d;

From the outlet screen 2 the liquor passes 40 I through pipe ill to circulation pump 9 and from the pressure side of the latter is conducted through heater H to pipe it, from which it is distributed between the inlet pipes 5 and It.

The distribution takes place by means of a it pivoted flap valve I3,which may be adjusted so as to completely close one or other of the pipes or as to keep both pipes partly open, so as to distribute the'liquor betweenv said pipes in the desired ratio.

The adjustment of flap valve 13 as mentioned above may take place manually in accordance 'with a predetermined diagram or may also take place automatically, either in accordance with a distribution curve predetermined for the complete 55 period of digesting or under the control of a temperature or pressure relay.

Although it will in many cases be preferable to providethe closing valves or cocks I or 8 even when the regulating valve I3 is used, these cocks I and I .may also be omitted, if so desired.

Referring to Figure 2 the digester I is provided with two annular outlet screens l4, l5, located on opposite sides of the-central transverse plane the digester, said screens being interconnected by means of an interior conduit ii. Said conduit is connected by means of a pipe l1 with the suction side of circulation pump 9.

At the junction between pipe i1 and conduit ii there is located an adjustable pivoted flap valve II, by means of which the pipe I! may be connected with one or the other of screens l4, IE, or if so desired with both screens.

At the top and bottom the digester is provided with intakes 3, 4 for digester liquor, said intakes being connected by means of pipes 5 and 6 and the adjusting flap valve. IS with the heating device ll, so that the liquor which is pressed through the heating device by means of pump 9 may be conducted to-the upper intake 3 or to the lower intake 4, or if so desired to both intake openings at any desired ratio.

In the position of the adjusting valves l8, l3

illustrated with full lines on the drawings the liquor is introduced into the digester through the top intake 3 and is taken out through the lower outlet screen IS, passing through the pulp approximately along the conical space defined by the dotted lines Ii. When the valves i8, I! are 'adjusted to the positions indicated with dotted, lines the liquor will be taken out through outlet screen l4 and introduced through bottom intake 4, passing through the pulp approximately as indicated by the dotted lines 20.

At the two above mentioned positions of valves [4,- l3 the current of liquor through the pulp will accordingly take place on intersecting paths, whereby the risk 01' forming permanent channels through the mass is avoided.

The formation of channels through the pulp will further be prevented thereby that the pulp is caused to perform some slight movements upon each change of current.

The two valves I8, it if desired may be mounted on a common valve spindle or interconnected by some suitable form of gear or lever mechanism, but they may also be adapted to be operated independently.

By repeated changing of intake and outlet alternating with the use of both intakes and outlets simultaneously it is possible to obtain a great variation in current directions and amounts of liquor circulating in each direction.

In accordance with the form illustrated on Figure 2 the pipes from the top of heater II to the top and bottom of the digester are located on the outside of the digester, but obviously these pipes may also be located inside the digester, in which case the adjusting valve I3 may be combined in any suitable manner with the adjusting valve I8.

I claim:

In a wood pulp digester, a system for positive circulation of the digesting liquor comprising a circulation pump, conduits for connecting the pressure side of said pump with the top and bottom intakes to the digester, an annular outlet screen in the upper portion of the digester, a second annular outlet screen in the lower portion of the digester, a conduit interconnecting said annular outlet screens at their peripheries and attached tovand contacting the inside wall of the digester, a conduit connecting said conduit interconnecting said annular outlet screens with the suction side of said circulation pump, a single controlling flap valve for distributing the liquor from said circulation pump between the conduits leading to the top and bottom intakes of the digester and a single controlling flap valve for connecting either or both annular outlet screens with thesuction side of said circulation pump whereby said digester interior is substantially unobstructed except for said screens.

EINAR MOR'I'ERUD. 

